1. Field of the Invention
This invention relates to lens blocking apparatuses and has particular reference to improvements in block casting fixtures.
2. Description of the Prior Art
In the blocking of lenses, particularly of the type formed of optical resins and commonly referred to as "plastic" lenses, difficulties have arisen from a need to meet at least two major requirements. These are: that despite variations in diametral sizes of lenses to be blocked, the blocks must in each case extend nearly from edge-to-edge for full surface support and prevention of lens warpage, fracturing or other damage during subsequent surface grinding and/or polishing operations; and that clamping forces applied to the lenses during blocking be adequate for secure holding purposes but otherwise minimal and so geometrically applied to the lenses, regardless of their diametral size, as to avoid distortion or other damaging of the lenses.
Corollary to the foregoing is the need to minimize the volume of blocking material used in each operation for heated metallic alloy or similar heated blocking operations so as to avoid lens warpage by overheating from the blocking medium.
In blocking lenses by the block casting technique, e.g. with a relatively low melting temperature metal alloy which is now widely used in the art, the aforesaid problems of avoiding lens warpage or other damage during blocking and working have hitherto been at least partially, but far less than efficiently, overcome by the provision of differently and separately designed and/or proportioned blocking fixtures for differently sized or diametrically dimensioned lenses. This requirement for the manufacture and supplying of a plurality of blocking fixtures for use with each lens blocker and their usual individual ungainliness and costliness, not to mention time spent in interchanging these fixtures during use of a blocker, renders such prior art blocking systems unduly expensive, ungainly, awkward and tedious to use and generally of less than optimum efficiency and/or efficacy.
It is, accordingly, a principal object of this invention to overcome the aforesaid and related problems and deficiencies in the field of lens blocking and more particularly in the area of in situ block casting operations.